President Barack Obama, stands with Health and Human Services Secretary Kathleen Sebelius and people who support the Affordable Care Act, his signature health care law, as he speaks in the Rose Garden of the White House in Washington. Congress plunged the nation into a partial government shutdown Tuesday as a long-running dispute over Obama's health care law forced about 800,000 federal workers off the job, suspending all but essential services. (ASSOCIATED PRESS / Charles Dharapak)

WASHINGTON (AP) — Hailing it as an “historic day,” President Barack Obama pressed forward his flagship health care program Tuesday, inaugurating new insurance exchanges to expand access for those without coverage despite the shutdown taking hold across much of the government.

Obama said the opportunity to access affordable insurance is life-changing for those who could not do so before the launch of the exchanges, now open for enrollment for six months starting Tuesday. As a sign of how eager Americans were to get started, Obama said more than 1 million people had visited the website before 7 a.m. EDT — exceeding expectations and, in some cases, slowing down the computer systems.

“This is life-or-death stuff,” Obama said in the White House Rose Garden, flanked by Americans who plan to enroll through the exchanges. He said tens of thousands of Americans die each year for lack of health insurance, and others go bankrupt. “Today we begin to free millions of our fellow Americans from that fear.”

Obama urged Americans to call in or go online, promoting an online system that he said will offer more choices, more competition and lower prices. For that to work, the Obama administration needs tens of millions of Americans — mostly younger, healthy people — to sign up of offset the costs of patients whose health care costs more.

Obama acknowledged there would be glitches in rolling out the program — there have been plenty already — but said that’s normal and that the problems will be fixed. The Obama administration hopes to sign up 7 million people during the first year.

Obama’s appearance kicked off a major campaign by his administration and its allies to enroll as many Americans as possible through the exchanges, a centerpiece of Obama’s health care law.

But any sense of festivity surrounding the opening of the exchanges was quickly eclipsed by the fact that throughout Washington and across the country, much of the federal government was shuttered. Congress, gridlocked over whether to dismantle the law, missed the midnight deadline to keep funding the government.

That meant that hundreds of thousands of federal workers were sent home — including many of Obama’s own aides. The White House cut its staff by three-quarters as first partial shutdown in almost two decades began.

That his health care law remained so contentious in Congress three years after he signed it was not lost on Obama. Visibly rankled by Republicans’ continued efforts to gut the law and use a shutdown as leverage, Obama denounced House Republicans for what he called an “ideological crusade to deny health insurance to millions of Americans.”

“This shutdown is not about deficits, it’s not about budgets,” Obama said. “It’s about rolling back our efforts to provide health insurance to folks who don’t have it. It’s about rolling back the Affordable Care Act.”

“This, more than anything else, seems to be what the Republican Party stands for these days,” he added.

Obama’s other message to Americans: Shutdown or not, the exchanges remain open. That’s because funding for much of the Affordable Care Act, like other “mandatory” functions such as Social Security, air traffic control and national defense, is protected from the whims of Congress.

“It is settled, and it is here to stay,” Obama said.

Obama was also deploying top deputies Tuesday to spread the message of newly available health care coverage, the White House said. Vice President Joe Biden will appear on college radio stations. First lady Michelle Obama is publishing an editorial on a women’s lifestyle website. And senior Obama adviser Valerie Jarrett and other officials will be guests on African-American radio shows.